Radio

Photo by: R-O-M-A

Radio is the technology that allows information to be transmitted and
received over radio waves. Radio makes it possible to establish wireless
two-way communication between individual pairs of transmitters/receivers
and it is used for one-way broadcasts to many receivers. Radio signals can
carry speech, music, or digitally encoded entertainment. Radio waves occur
naturally in space or can be created by people. They are a long-wave form
of electromagnetic radiation, or radiation that transmits energy through
the interaction of electricity and magnetism.

The history of radio

In the nineteenth century, Scottish physicist James Clerk Maxwell
(1831–1879) developed a mathematical theory proving that magnetism
and electricity were related. His theory linking the two forces became
known as the electromagnetic theory. He predicted that light is only one
type of electromagnetic radiation and that wavelengths should exist below
infrared (those situated outside the visible spectrum at the red or
long-wavelength end) and above ultraviolet (situated outside the visible
spectrum at the violet or short-wavelength end). In the 1880s, German
physicist Heinrich Hertz (1857–1894) discovered extremely
long-wavelength radio waves, proving Maxwell's theory.

Italian physicist and engineer Guglielmo Marconi (1874–1937),
fascinated with Hertz's discovery of radio waves, built his first
crude radio transmitter and receiver in 1895. In 1901, using his
"wireless" (as radio was called then), he sent the first
message via signals similar to Morse code (which uses dots and dashes for
letters and numbers) across the Atlantic Ocean. In the succeeding years,
other scientists improved on Marconi's invention, and it eventually
became possible to send voice signals by radio waves.

Radio broadcasting as we know it today began in 1920. Station KDKA in
Pittsburgh, Pennsylvania, made the announcement to the few people who
owned radio receivers that Warren G. Harding had been elected president of
the United States. Within a few years, many homes had radio receivers and
several radio stations scheduled regular programming.

Radio waves and frequencies

Although turning on a radio produces sound, radio waves themselves cannot
be "heard" and have nothing to do with sound waves. While
sound waves are a vibration of the air, radio waves are electromagnetic
and a part of the light spectrum. Radio waves travel at a speed of 186,282
miles
(299,727 kilometers) per second—the speed of light. Radio waves
travel through the air, surrounding us with vibrations that can only be
detected through a radio receiver.

Radio programs begin as sound waves, which microphones change into
electrical signals. From the antenna atop the radio station, the
electrical signals are broadcast as electromagnetic waves. The receiver
picks up the waves in the air, electrically amplifies (enlarges) them, and
converts them back into sound through the speaker of the radio in your
home.

Although radio waves from many stations surround us all the time, the
radio does not receive them all at the same time because the stations
broadcast at different frequencies. A frequency is the number of times per
second that radio waves vibrate. The numbers on a radio dial represent the
frequencies used by radio stations in your area. For example, if the dial
is set at 96, the radio signal you hear is broadcasted at 960 kilocycles,
or 960,000 cycles per second.

Words to Know

Carrier wave:
Radio signal with superimposed information.

Electromagnetic radiation:
Radiation that transmits energy through the interaction of electricity
and magnetism.

Infrared radiation:
Electromagnetic radiation of a wavelength shorter than radio waves but
longer than visible light that takes the form of heat.

Modulation:
Process by which a characteristic of radio waves, such as amplitude or
frequency, is changed to make the waves correspond to a signal or
information that is being transmitted.

Ultraviolet radiation:
Electromagnetic radiation of a wavelength just shorter than the violet
end of the visible light spectrum.

Wavelength:
The distance between two peaks in any wave.

Modulation

A radio signal alone, without information (speech, music) added to it, is
called a carrier wave. Adding information to a carrier signal is a process
called modulation. The simplest modulation method is to vary the strength
of the signal. The result is called amplitude modulation, or AM.
The method that varies the signal's frequency is known as
frequency modulation, or FM. AM radio waves are about 1,000 feet (1,600
kilometers) in wavelength, while FM radio waves are only a few feet in
wavelength. Broadcasts on AM radio stations can often be heard for
hundreds of miles, especially at night when electromagnetic interference
is minimal. Broadcasts on FM stations do not travel such a distance, but
they have better sound quality and are not affected by lightning-caused
static that often plagues AM broadcasts.